When Daniel Lieberman, Ph.D., observes people eating, running, or working, he sees a prehistoric body not yet caught up with its modern environment. An evolutionary physiologist at Harvard University, Lieberman argues that we haven’t evolved for fast food, padded shoes, or even antibiotics, and our health is suffering for it. We talk to Lieberman about his new book, ‘The Story of the Human Body,’ a manifesto for how to live a bit more like our ancient ancestors.

Though it has taken an epoch for us to evolve, you argue that the past couple hundred years have changed everything. How?Cultural evolution is more powerful and faster than biological evolution. Some rapid changes to our environments have been beneficial – like antibiotics, sterilization, and agriculture – but benefits almost always come with costs, like a loss of helpful bacteria and a rise in diabetes and obesity. An evolutionary perspective helps us remember what is actually normal and reminds us that we live in a largely abnormal state.

Why do you say obesity is the great crisis of our time?A lot of serious diseases that are chronic and noninfectious are obesity related. But obesity is just a symptom of the cause of those diseases – which is getting too much energy from abundant food. We have created an environment that makes people sick through a surfeit of energy. You can use this energy to maintain your body, and you can use it to grow and reproduce, but you can only grow or reproduce so much.

You say humans have evolved for endurance activities. How so?From an evolutionary perspective, we’re selected more to be endurance athletes than power athletes. Since the origins of hunting and gathering two million years ago, a typical man would have walked or run maybe nine miles a day, and farther when hunting. Let’s face it, we’re not hunter-gatherers anymore; people have different lifestyles, and not everybody can do what’s natural. I’m lucky; I have enough time to go for long runs and like them. Not everyone has time to train for an Ironman.

How is technology at odds with our biology?Temperature is one example. Children who don’t experience heat don’t sweat as effectively. So if you grew up in air-conditioning, you’re not going to sweat as well. Now, that helps you if you grew up in the Arctic, but not if you grew up in the South and all of a sudden there’s a heat wave and you’ve lost air-conditioning for a week. The body is filled with physiological and anatomical structures that require some degree of stress, and some degree of a response to a particular stressor for appropriate and normal growth.

You are a barefoot runner. Are shoes really an unnecessary technology?Putting arch supports in our shoes means the foot muscles don’t have to grow properly. And guess what? Thirty percent of Americans get flat feet. Of course, people think the reverse, that if you just take off your shoes and go barefoot, you’ll be miraculously cured of every ill in your body, which, of course, is not true. None of these things are panaceas.